The present invention relates to apparatus for producing sample ions, making it ideally suited for use with a mass spectrometer.
Prior to this invention, the present inventor had proposed a new apparatus and method for producing sample ions, both of which are fully disclosed in Japanese Patent Application No. 53-80960. A cross section of this apparatus is shown in FIG. 1.
As shown in FIG. 1, a carrier gas, such as Argon, is introduced into a glass tube 1 through a supply tube 2. One end of the glass tube 1 is closed by an insulating stopper 3, through which a needle-shaped electrode 4 is inserted into the glass tube 1. In said glass tube 1, a counter electrode 5, which is opposite the electrode 4, a mesh electrode 6, and a repeller electrode 7 are arranged in this order, between which insulating rings 8 and 9 are inserted. An emitter 10 is supported by an insulating base 11 and is inserted into the glass tube 1 through an opening in the side wall of the glass tube 1.
The method of using the apparatus shown in FIG. 1 comprised the following steps:
(a) by producing Argon ions (Ar.sup.+), electrons (e.sup.-) and excited Argon atoms (AR*: metastable species) by corona discharges between the needle electrode 4 and the counter electrode 5; PA1 (b) by removing Ar.sup.+ and e.sup.- by the electrodes 5 and 6; and PA1 (c) by ionizing a sample on the emitter 10 by the internal energy of AR*, said energy is transferred to the sample at the time that Ar* come into contact with the sample. PA1 (a) liquid samples can be directly ionized under atmospheric pressure; PA1 (b) by using Argon as the carrier gas, most of the organic compounds can be ionized; PA1 (c) since ionization is performed under atmospheric pressure, sample handling is easy; and PA1 (d) since a vacuous state is not essential, the structure of the apparatus can be simplified.
The following advantages can be realized with this method and apparatus:
In case the proposed apparatus is combined with a mass spectrometer, it is necessary to generate a large quantity of sample ions and to effectively introduced them into the mass spectrometer. Therefore, the present inventor has tried to use an FD (Field Desorption) emitter which comprises a wire having a large number of whiskers, as the emitter 10. It is not possible, however, to fully satisfy such requirements.